This invention relates to fastening elements and, more particularly, to a fastening element having an anti-jacking device for fastening a concave member to the surface of a second member.
Molded plastic fastening elements are rapidly gaining commercial acceptance both here and abroad. Such fastening elements typically comprise a head for disposition in one end of an opening, expansible locking means for location at the other end of the opening, and connector means extending therebetween. The connectors can be flexible spaced apart connectors connected to the expansible locking means at positions wherein they are radially outward of the openings in the expanded condition, such as is disclosed in U.S. Pat. No. 3,651,634 issued to the present inventor on Mar. 28, 1972. Alternatively, the connectors can be connected to the locking means at positions radially adjacent the openings such as is disclosed in applicant's copending application Ser. No. 826,865 filed Aug. 22, 1977.
In many uses, the fastening element in its collapsed condition is inserted through an opening of a first member, such as a sheet of wallboard, and opened to its expanded condition to fasten to the member. A second member is then attached to the first by a threaded screw extending through the second member and into the fastening element. A screw of appropriate length can also ensure that the expansible locking means remains in its expanded condition.
While such arrangement works well for many applications, problems are encountered when the second member fastened by the screw presents a concave surface facing the fastening element. In such instances, the turning of the screw tends to "jack" the fastener from the first member with the large mechanical advantage provided by the threaded screw and to pull the fastener into the open space bounded by the concave surface and the first member. Such problems are typically encountered, for example, in attempting to fasten concave shelving supports to walls. The result is a substantially weakened fastening arrangement potentially subject to premature failure.
Accordingly, there is a need for an improved fastening arrangement to permit fastening of concave members.